1. Field of the Invention
The present invention relates to a slider of a thin-film magnetic head which comprises a medium facing surface that faces toward a recording medium and a thin-film magnetic head element located near the medium facing surface, and to a method of manufacturing such a slider.
2. Description of the Related Art
Performance improvements in thin-film magnetic heads have been sought as areal recording density of hard disk drives has increased. Such thin-film magnetic heads include composite thin-film magnetic heads that have been widely used. A composite head is made of a layered structure including a recording head having an induction magnetic transducer for writing and a reproducing head having a magnetoresistive (MR) element for reading. MR elements include an anisotropic magnetoresistive (AMR) element that utilizes the AMR effect and a giant magnetoresistive (GMR) element that utilizes the GMR effect. A reproducing head using an AMR element is called an AMR head or simply an MR head. A reproducing head using a GMR element is called a GMR head. An AMR head is used as a reproducing head where areal density is more than 1 gigabit per square inch. A GMR head is used as a reproducing head where areal density is more than 3 gigabits per square inch. It is GMR heads that have been most widely used recently.
The performance of the reproducing head is improved by replacing the AMR film with a GMR film and the like having an excellent magnetoresistive sensitivity. Alternatively, a pattern width such as the reproducing track width and the MR height, in particular, may be optimized. The MR height is the length (height) between an end of the MR element located in the air bearing surface and the other end. The air bearing surface is a surface of the thin-film magnetic head facing toward a magnetic recording medium.
Performance improvements in a recording head are also required as the performance of a reproducing head is improved. It is required to increase the linear density in order to increase the areal density among the performance characteristics of the recording head. To achieve this, it is required to implement a recording head of a narrow track structure wherein the width of top and bottom poles sandwiching the recording gap layer on a side of the air bearing surface is reduced down to microns or a submicron order. Semiconductor process techniques are utilized to implement such a structure. A pattern width, such as the throat height in particular, is also a factor that determines the recording head performance. The throat height is the length (height) of pole portions, that is, portions of magnetic pole layers facing each other with a recording gap layer in between, between the air-bearing-surface-side end and the other end. A reduction in throat height is desired in order to improve the recording head performance. The throat height is controlled by an amount of lapping when the air bearing surface is processed.
As thus described, it is important to fabricate well-balanced recording and reproducing heads to improve the performance of the thin-film magnetic head.
In order to implement a thin-film magnetic head that achieves high recording density, the requirements for the reproducing head include a reduction in reproducing track width, an increase in reproducing output, and a reduction in noise. The requirements for the recording head include a reduction in recording track width, an improvement in overwrite property that is a parameter indicating one of characteristics when data is written over existing data, and an improvement in nonlinear transition shift.
In general, a flying-type thin-film magnetic head used in a hard disk device and the like is made up of a slider, a thin-film magnetic head element being formed at the trailing edge of the slider. The slider slightly flies over a recording medium by means of the airflow generated by the rotation of the medium.
Reference is now made to FIG. 21A to FIG. 24A, FIG. 21B to FIG. 24B, and FIG. 25 to describe an example of a method of manufacturing a related-art thin-film magnetic head element. FIG. 21A to FIG. 24A are cross sections each orthogonal to the air bearing surface. FIG. 21B to FIG. 24B are cross sections of the pole portion each parallel to the air bearing surface.
According to the manufacturing method, as shown in FIG. 21A and FIG. 21B, an insulating layer 102 made of alumina (Al2O3), for example, having a thickness of about 5 to 10 μm, is deposited on a substrate 101 made of aluminum oxide and titanium carbide (Al2O3—TiC), for example. Next, on the insulating layer 102, a bottom shield layer 103 made of a magnetic material is formed for a reproducing head.
Next, a bottom shield gap film 104 made of an insulating material such as alumina and having a thickness of 100 to 200 nm, for example, is formed through sputtering on the bottom shield layer 103. On the bottom shield gap film 104, an MR element 105 for reproduction having a thickness of tens of nanometers is formed. Next, a pair of electrode layers 106 are formed on the bottom shield gap film 104. The electrode layers 106 are electrically connected to the MR element 105.
Next, a top shield gap film 107 made of an insulating material such as alumina is formed through sputtering, for example, on the bottom shield gap film 104, the MR element 105 and the electrode layers 106. The MR element 105 is embedded in the shield gap films 104 and 107.
Next, on the top shield gap film 107, a top-shield-layer-cum-bottom-pole-layer (called a bottom pole layer in the following description) 108 is formed to a thickness of about 3 μm. The bottom pole layer 108 is made of a magnetic material and used for both the reproducing head and the recording head.
Next, as shown in FIG. 22A and FIG. 22B, a recording gap layer 109 made of an insulating film such as an alumina film and having a thickness of 0.2 μm is formed on the bottom pole layer 108. Next, the recording gap layer 109 is partially etched to form a contact hole 109a for making a magnetic path. Next, a top pole tip 110 for the recording head is formed on the recording gap layer 109 in the pole portion. The top pole tip 110 is made of a magnetic material and has a thickness of 0.5 to 1.0 μm. At the same time, a magnetic layer 119 made of a magnetic material is formed for making the magnetic path in the contact hole 109a for making the magnetic path.
Next, as shown in FIG. 23A and FIG. 23B, the recording gap layer 109 and the bottom pole layer 108 are etched through ion milling, using the top pole tip 110 as a mask. As shown in FIG. 23B, the structure is called a trim structure wherein the sidewalls of the top pole portion (the top pole tip 110), the recording gap layer 109, and a part of the bottom pole layer 108 are formed vertically in a self-aligned manner.
Next, an insulating layer 111 of alumina, for example, having a thickness of about 3 μm is formed over the entire surface. The insulating layer 111 is polished to the surfaces of the top pole tip 110 and the magnetic layer 119 and flattened.
On the flattened insulating layer 111 a first layer 112 of a thin-film coil, made of copper (Cu), for example, is formed for the induction-type recording head. Next, a photoresist layer 113 is formed into a specific shape on the insulating layer 111 and the first layer 112 of the coil. Heat treatment is performed at a specific temperature to flatten the surface of the photoresist layer 113. Next, a second layer 114 of the thin-film coil is formed on the photoresist layer 113. Next, a photoresist layer 115 is formed into a specific shape on the photoresist layer 113 and the second layer 114 of the coil. Heat treatment is performed at a specific temperature to flatten the surface of the photoresist layer 115.
Next, as shown in FIG. 24A and FIG. 24B, a top pole layer 116 for the recording head is formed on the top pole tip 110, the photoresist layers 113 and 115 and the magnetic layer 119. The top pole layer 116 is made of a magnetic material such as Permalloy (NiFe). Next, an overcoat layer 117 of alumina, for example, is formed to cover the top pole layer 116. Finally, machine processing of the slider including the forgoing layers is performed to form the air bearing surface 118 of the recording head and the reproducing head. The thin-film magnetic head element is thus completed.
FIG. 25 is a top view of the thin-film magnetic head element shown in FIG. 24A and FIG. 24B. The overcoat layer 117 and the other insulating layers and films are omitted in FIG. 25.
Reference is now made to FIG. 26 to FIG. 28 to describe the configuration of the slider and a method of manufacturing the same. FIG. 26 is a bottom view that illustrates an example of the configuration of the air bearing surface of the slider. As shown, the air bearing surface of the slider 120 is shaped such that the slider 120 slightly flies over a recording medium such as a magnetic disk by means of the airflow generated by the rotation of the medium. In FIG. 26 numeral 121a indicates a convex portion and numeral 121b indicates a concave portion. A thin-film magnetic head element 122 is located near the air-outflow-side end of the air bearing surface of the slider 120 (that is, on the upper side of FIG. 26). The configuration of the head element 122 is as shown in FIG. 24A and FIG. 24B, for example. Portion A of FIG. 26 corresponds to FIG. 24B.
The slider 120 is fabricated as follows. A wafer includes a plurality of rows of portions to be sliders (hereinafter called slider portions) each of which includes the thin-film magnetic head element 122. This wafer is cut in one direction to form blocks called bars each of which includes a row of slider portions. Each of the bars is then lapped to form the air bearing surface. Furthermore, the convex portions 121a and the concave portion 121b are formed. Each of the bars is then divided into sliders 120.
FIG. 27 is a cross-sectional view taken along line 27—27 of FIG. 26. FIG. 27 illustrates only the main part of the thin-film magnetic head element 122. As shown in FIG. 27, the greater part of the slider 120 is made up of the substrate 101 of aluminum oxide and titanium carbide, for example. The rest of the slider 120 is made up of the insulating layer 127 of alumina, for example, and the head element 122 and so on formed in the insulating layer 127. The greater part of the insulating layer 127 is the overcoat layer 117.
As disclosed in Published Unexamined Japanese Patent Application Hei 9-63027 (1997), for example, a protection film of a material such as diamond-like carbon (DLC) may be formed on the air bearing surface of the slider 120 in order to prevent corrosion, for example, of the bottom shield layer 103, the bottom pole layer 108, the top pole tip 110, and the top pole layer 116 and so on. FIG. 28 is a cross-sectional view that illustrates the slider 120 with a protection film 128 formed on the air bearing surface, the slider 120 slightly flying over a recording medium 140.
In order to improve the performance characteristics of a hard disk device, such as areal recording density, a method of increasing linear recording density and a method of increasing track density may be taken. To design a high-performance hard disk device, specific measures taken for implementing the recording head, the reproducing head or the thin-film magnetic head as a whole depend on whether linear recording density or track density is emphasized. That is, if priority is given to track density, a reduction in track width is required for both recording head and reproducing head, for example.
If priority is given to linear recording density, it is required for the reproducing head to improve the reproducing output and to reduce a shield gap length, that is, the distance between the bottom shield layer and the top shield layer. Moreover, it is required to reduce the distance between the recording medium and the thin-film magnetic head element (hereinafter called a magnetic space).
A reduction in magnetic space is achieved by reducing the amount of flying of the slider. A reduction in magnetic space contributes not only to an improvement in the reproducing output of the reproducing head but also to an improvement in the overwrite property of the recording head.
The following is a description of the problem that arises when the magnetic space is reduced. In the prior art, lapping of the air bearing surface of the slider 120 has been performed on a rotating tin surface plate through the use of diamond slurry, for example.
A plurality of materials that make up the slider 120 have different hardnesses. For example, a comparison is made between: aluminum oxide and titanium carbide that is a ceramic material used for the substrate 101; a magnetic material such as NiFe used for the bottom shield layer 103, the bottom pole layer 108, the top pole tip 110, the top pole layer 116 and so on; and alumina used for the insulating layer 127. The hardness of aluminum oxide and titanium carbide is the greatest while that of NiFe is the smallest. The hardness of alumina is smaller than that of aluminum oxide and titanium carbide, and greater than that of NiFe.
The slider 120 includes a plurality of layers having different hardnesses as thus described. If this slider 120 is lapped on a tin surface plate through the use of diamond slurry as an abrasive, differences in level may result among the layers having different hardnesses. For example, as shown in FIG. 27, a difference of about 1 to 2 nm in level is created between the insulating layer 127 and the top pole layer 116, for example, that is a layer made of a magnetic material such as NiFe, an end of the top pole layer 116 being located behind an end of the insulating layer 127. A difference of about 4 to 5 nm in level is created between the insulating layer 127 and the substrate 101, an end of the insulating layer 127 being located behind an end of the substrate 101. In this case, the difference in level is about 5 to 7 nm between the surface of the thin-film magnetic head element 122 closer to the air bearing surface and the surface of the substrate 101 closer to the air bearing surface, the protection film 128 being excluded.
As shown in FIG. 28, the distance between the slider 120 and the recording medium 140 when the slider 120 is flying is about 7 to 9 nm. If the protection film 128 is provided, the distance between the recording medium 140 and the surface of the thin-film magnetic head element 122 closer to the air bearing surface increases by about 4 to 5 nm which corresponds to the thickness of the protection film 128. In view of the foregoing, the magnetic space, that is, the distance between the medium 140 and the surface of the head element 122 closer to the air bearing surface when the slider 120 is flying, is about 15 nm. When the magnetic space is of such a degree, attainable areal density is limited to about 80 to 100 gigabits per square inch.
As thus described, the related-art thin-film magnetic head may have a difference in level in the air bearing surface of the slider 120, the portion corresponding to the head element 122 being recessed behind the other part. As a result, it is difficult to reduce the magnetic space, and to improve the recording density.
Since it is difficult to reduce the magnetic space of the related-art thin-film magnetic head as described above, it is impossible to improve the performance of the reproducing head in particular to a sufficient degree, such as an improvement in the reproducing output and a reduction in half width of the reproducing head. As a result, the problem of the related art is that the error rate of the hard disk devices for high density recording increases and the yield of the hard disk devices decreases.
In Published Unexamined Japanese Patent Application Hei 7-230615 (1995), a technique is disclosed to flatten the flying surface of the slider, wherein a protection film made of an insulating film is provided in a recess produced between the slider and the head element when the flying surface of the slider is processed. In this publication the following first and second methods are disclosed to provide the protection film in the recess. The first method is to form a protection film through sputtering over the entire surface including the flying surface of the slider and a surface of the head element located closer to the flying surface, and to lap the flying surface of the slider so as to remove a portion of the protection film on the flying surface of the slider. The second method is to form a photosensitive organic film over the entire surface including the flying surface of the slider and a surface of the head element located closer to the flying surface; then to expose only a portion of the organic film on the surface of the head element; and then to remove the portion of the organic film. A protection film is then formed over the entire surface through sputtering, and the rest of the organic film is finally removed.
Nevertheless, the technique described in Published Unexamined Japanese Patent Application Hei 7-230615 has a problem that the magnetic space cannot be reduced because the flying surface of the slider and the surface of the head element located closer to the flying surface still have a difference in level.
Furthermore, according to the related-art thin-film magnetic head, since the slider 120 includes a plurality of layers having different hardnesses, lapping of the slider 120 can cause a smear on the reproducing head, which can result in a defect in the reproducing head. Hereinafter, this problem will be described in detail.
For the purpose of reducing the half width of the reproducing output, a shield gap length that is the distance between the bottom shield layer and the top shield layer has been reduced to the order of 70 to 80 nm. The MR element 105, the electrode layers 106 connected to the MR element 105, and the shield gap films 104 and 107 sandwiching these elements from above and below are interposed between the bottom shield layer and the top shield layer. The shield gap films 104 and 107 each have a thickness of 20 to 40 nm, for example. The MR element 105 has a thickness of 30 to 35 nm, for example.
The slider 120 is lapped, with the MR element 105 the electrode layers 106, and the shield gap films 104 and 107 exposed in the air bearing surface. In the slider 120, the substrate 101 made of aluminum oxide and titanium carbide, for example, has the greatest hardness, while the magnetic layers included in the thin-film magnetic head element 122 have the smallest hardness. The insulating layer 127 made of alumina, for example, has a hardness smaller than that of the substrate 101 and greater than that of the magnetic layers. When lapping such a slider 120 including a plurality of layers having different hardnesses, the slider 120 must be lapped with a greater load applied thereto, so as to lap the hard substrate 101. Then, during the lapping of the slider 120, chippings of the electrode layers 106 made of soft metal such as Au and Cu may be jammed and spread between the air bearing surface and the surface plate, producing a defect called a smear. The smear sometimes causes an electric short circuit between the MR element 105 and the bottom shield layer or the top shield layer. The short circuit can lower the sensitivity of the reproducing head and produce noise in the reproducing output, thereby deteriorating the performance of the reproducing head.